The invention relates to a gas-conducting device having pressure compensation as described in claim 1 and to the use of such a gas-conducting device as an exhaust-gas-recirculation valve and as an air-conducting means for an internal combustion engine having a charge-air device.
Spark-ignition and diesel engines, in particular those of motor vehicles, are normally provided with gas-conducting devices, in particular exhaust-gas-recirculation valves (EGR valves). They partly admix exhaust gas with the fresh intake gas in order to reduce the NOx emission and also to improve the fuel consumption and reduce the generation of noise. Furthermore, there are air-conducting devices, in particular in connection with charge-air devices of internal combustion engines.
Such gas-conducting devices comprise metering elements or control elements, with which the quantity of conducted or recirculated gas can be set as a function of the operating point. Too little gas recirculation would fail to have the desired effects; too much gas recirculation, in the case of exhaust-gas recirculation in spark-ignition engines, would lead to malfunctions or to an undesirable increase in HC or even CO emissions and, in diesel engines, would lead to an undesirable increase in the particle emissions; and too much air recirculation would make the desired charge state unattainable.
Such control elements are as a rule valves which can be closed completely and which are set by a vacuum diaphragm or a servomotor or a proportional magnet working against a spring, which in turn are actuated via a timing valve or a relay from the control unit of the engine. The information used for this purpose in the control unit generally concerns the load and speed of the engine and the air quantity drawn in. To improve the functioning, the feedback of the opening travel via a displacement measuring system is also applied.
Acting on the gas-conducting devices is a pressure gradient, which as a rule exists between the pipe systems of the engine which are connected to them. It poses a problem for the actuation of the metering element of the gas-conducting device inasmuch as it generally attempts to move the metering element in the direction in which the conducted or recirculated gas also flows.
It is an object of the invention to provide a gas-conducting device in which the actuation of the valve is as far as possible independent of the aforesaid pressure fluctuations acting on the gas-conducting device.
The object is achieved by a gas-conducting device having the features specified in claim 1.
According to the invention, a gas-conducting device for internal combustion engines, in particular motor vehicle engines, comprises a pressure duct, a fresh-gas duct feeding fresh gas, an outlet duct and an orifice opening into the fresh-gas duct and the outlet duct, at least the pressure duct and the orifice being connected to one another via a control element for metering or controlling gas, in particular air or exhaust gas, and a compensating device being provided in order to compensate for forces which act on the control element on account of a pressure difference between gas pressures on the pressure-gas side and gas pressures on the fresh-gas side. The aforesaid effect of the pressure gradient is therefore minimized and preferably completely compensated for by the provision according to the invention of the compensating device. Consequently, the invention enables, in particular, an actuating device of the control element to be dimensioned so as to be correspondingly smaller, resulting in a saving in space and weight, lower power consumption and less self-heating. The pressure gradient of the gas pressure across the control element, on account of this compensating device, cannot lead to a force component which acts in the direction of undesirable opening or closing of the control element, as a result of which the desired control of the gas quantity fed through is considerably improved.
In a preferred embodiment of the invention, one side of the compensating device is acted upon with the gas pressure on the pressure-gas side and the other side is acted upon with the gas pressure on the fresh-gas side. The resulting pressure difference via the compensating device results in a force component which is opposed to the force component to be compensated, has the same magnitude and therefore effects the balancing of the two force components.
The compensating device may advantageously be provided as a butterfly valve, a double, ball, cone or cylinder valve in the control element.
In a further preferred embodiment, the control element comprises a valve rod and a valve disk secured thereto and having a gas-pressure-effective area, so that a valve-disk force acts on the valve disk, this valve-disk force being equal to the product of the gas-pressure-effective area and the pressure difference. The compensating device comprises at least one piston, one diaphragm and/or one bellows, which is secured to the valve rod and on whose gas-pressure-effective area the pressure difference acts, so that a compensating force which compensates for the valve-disk force acts on the valve rod.
In a further preferred embodiment, the control element is actuable by a mechanical, pneumatic, hydraulic, magnetic or electric actuating device or servomotor, in particular an electric actuating magnet. The use of a magnet or proportional magnet has proved to be especially advantageous, since the opening or position of the control element can be set very quickly and accurately by such a magnet. Since the actuating force in a proportional magnet is determined approximately only by the current flowing through and not by the opening travel, a quick reaction to control signals is advantageously also possible.
In a further preferred embodiment, the compensating device comprises an inner valve which is provided in the control element.
A gas pressure in an inner-valve compensating space is advantageously controllable via the inner valve in combination with an opening gap between a piston of the compensating device and a guide sleeve of the piston, and the inner valve is actuable by an actuating device and/or an inner-valve actuating device. The selection of the diameter of the piston relative to that of the control element, for example of the main valve, also influences the matching of the inner valve to the opening gap between the piston and the guide sleeve.
In a further preferred embodiment, the compensating device acts on the control element via a kinematic transmission, in particular a lever transmission, in order to compensate for a difference between, on the one hand, areas of the control element which are effective for the gas pressure and, on the other hand, the compensating device. This transmission converts the force component produced by the compensating device to a magnitude which is suitable for compensating for the force to be compensated on the control element. This is especially advantageous if the areas of compensating device and control element which are effective for the gas pressures differ from one another.
In a preferred embodiment, the control element is prestressed in the closing direction by a spring action of a diaphragm or a bellows, in which case a spring, in particular, can be additionally provided for assisting the prestressing in order to produce an additional force component in the closing direction of the control element.
In a preferred embodiment of the invention, the compensating device and the control element are connected to one another in such a way as to be effective in terms of force and are controllable via the actuating device. In this way, the forces produced by the compensating device and by the actuating device can act jointly on the control element and can be suitably added to one another or can suitably compensate for one another in order to exert the desired net force or force component on the control element.
In a further embodiment, the control element has a device, e.g. a potentiometer, which at any time provides information on the respective opening cross section of the control element. Thus the control-element opening set by the actuating device can be compared with a desired opening.
According to a further aspect of the invention, the invention relates to the use of a gas-conducting device according to the invention as an air-conducting device in an internal combustion engine having a charge-air device, the pressure duct in this case being a fresh-air pressure duct which opens into a compressor outlet duct of a compressor of the charge-air device, the outlet duct being a compressor inlet duct of the compressor, and the fresh-gas duct being a fresh-air duct, and the control element being designed for metering air. Such use of the gas-conducting device as an air-conducting device also advantageously permits an air flow from the fresh-air duct into the fresh-air pressure duct through the control element, if a lower gas pressure prevails in the fresh-air pressure duct than in the fresh-air duct.
According to a further aspect of the invention, the invention relates to the use of the gas-conducting device according to the invention as an exhaust-gas-recirculation device for internal combustion engines,.the pressure duct in this case being an exhaust-gas duct and the control element being designed for metering exhaust gas from the exhaust-gas feed duct into the orifice and thus recirculating exhaust gas into a gas flow in the outlet duct, which opens into the gas feed of the internal combustion engine.